The present invention relates to a cop preparation device for a bobbin-winding machine.
When the winding of cops on a ring spinning machine has been completed, the trailing yarn end is generally fixed or secured in position by forming a reserve winding extending downward to the tube foot before the spinning cops are doffed. However, the yarn end fixed at the tube foot cannot be reached by a grasping tube in the bobbin-winding machine which supplies the yarn end of a yarn connection device from a feeding or delivery bobbin and which fetches the yarn end of a freshly replaced cop for piecing-up the yarn.
For this reason a so-called preparation device is provided in bobbin-winding machines for detaching the reserve winding from the foot end of cops and placing the yarn end in a few windings on the upper tip end of the cop tube tip. From such disposition, the upper yarn end windings are blown off at the winding head, drawn into the grasping tube by suction and grasped. However, the preparation device can also be arranged to place the yarn end at any other defined position on the cop, e.g. inside the tube or on the circumferential surface of the yarn body.
DE 44 24 462 A1 teaches a cop preparation device operative to place the reserve winding of yarn as an upper winding. The cop to be prepared is positioned on a suction device adjacent to a suction tube having a slot on the side facing the spinning cop for drawing in the yarn end by suction and taking it up until it is laid down on the tube tip.
A blocking device for cutting the suction air on and off is arranged in the suction tube. The suction flow through the slot of the suction tube acts from point in time of the drawing in of the yarn end by suction until the point in time at which the yarn end has been wound onto the tube tip. The vacuum must be sufficiently great that the yarn end is loosened from the cop and drawn into the suction tube, which can be difficult for example in the case of stiff linen yarns. On the other hand, the yarn must not become frayed by the suction in the case of sensitive or fragile yarns. The yarn must not be held too slackly during the winding of the upper winding in order that the yarn windings remain on the tube tip.